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LMP8645: offset error

Marcello Deluca
Prodigy 210 points
Part Number: LMP8645

Is the TI spice model for the LMP8645 wrong? Using TI spice, I get an unexpectedly large offset error; I didnt expect this for a part with specs of Vos = 1mV and Ib = 23uA.

Using high side current sensing through a .005 ohm sense resistor as shown below, the result is about 60mV on the output when the load current is very low. For example sweeping R2 (in my cct below) from 50 ohms down to to 1 ohm (corresponding to load current of 240mA to 12A) the output sits at about 60mV until the load reaches / exceeds about 1.5A then starts to rise (reaches 82mV @ 12A).

  • 0
    TI__Mastermind 29710 points

    Hello Marcello,

    I think this matches closer to the diagrams on figure 8-2 and 8-3 at low input.  I will get some lab data to see if this is the case from one of the units I can acquire here.

  • 0 in reply to Javier Contreras4
    Prodigy 210 points

    I think it may be caused by input offset current which is not included in data sheet.. If I assume the 60mV output I get with no load current is caused by offset current on the device inputs, that would amount to about 12uA. The spec sheet does state input bias current is12uA (typ.) but I would expect the bias offset current to be much less. If the 12uA is differential bias current then that explains the 60mV output.

  • 0 in reply to Marcello Deluca
    TI__Mastermind 29710 points

    Marcello,

    I think you are correct.  I looked in the lab after I got an EVM and I saw similar results and error changing with the VCM.  

    I would recommend going with one of our newer devices that does not have this issue.  From most of the specifications I would recommend the INA296A1 or INA296B1.  If you give me more details on your requirements I think I can make other recommendations.